The present invention relates to heat transfer in Jet engine components and, more particularly, to an improved impingement heat transfer assembly for use in jet engines.
Impingement cooling systems are commonly used in gas turbine engines. Typically, a perforated liner spaced from a heated member, such as a shroud, directs cooling air substantially normally to the surface of the shroud in order to enhance turbulence and improve the convective heat transfer coefficient at the surface. U.S. Pat. No. 3,388,888, issued to Kercher et al., and assigned to the General Electric Company, discloses impingement cooling for providing high heat transfer coefficients at the leading edge of turbine vanes. U.S. Pat. No. 3,800,864, issued to Hauser et al., and assigned to the General Electric Company, teaches that impingement of cooling air on a smooth surface is known. Hauser teaches that impingement is disadvantageous due to blockage of the liner perforations and inefficient use of cooling air. (Col. 4, line 1-6.) Hauser proposes a plurality of protuberances or pin-fine extending from a face, and an aperture for flowing cooling air over the face in parallel or counterflow heat transfer relationship (Col. 4, lines 28-42, Col. 5.) The protuberances serve the function of increasing the effective convective heat flow area and perform the function performed by the liner apertures in the known impingement systems. (Col 4, lines 31-37.) The arrangement of protuberances can be varied as to quantity per unit area. (Col 4, lines 64-66.)
U.S. Pat. No. 4,934,145, issued to Zeisser, discloses a combustor heat shield assembly where cooling air is impinged on the back of a plate, and is then directed by ridges to flow outward parallel to the back of the plate to enter a region which includes a plurality of individual pin fins extending from the back of the plate. (Col. 3, lines 29-53.)
U.S. Pat. No. 4,916,905, issued to Hayercroft et al., discloses a first perforated member and a second member including a large number of projections extending from the second member to positions closely adjacent the first member. (Col. 2, lines 30-40.) Cold air flows through perforations in the first member and onto and around the projections. (Col. 2, lines 45-50.) The spacing between the first and second members must be sized sufficiently large to accommodate flow of the cooling flow between the two members. Therefore, because the projections extend closely adjacent the first member, the projection height above the second member will be relatively large. Also, Havercroft mandates that the projections should not be aligned with the perforations in the first member, because projections closely spaced from the first member and aligned with the perforations would block the flow exiting the perforations.
U.S. Pat. No. 4,864,827, issued to Richardson et al., discloses first and second combustor skins spaced apart by a plurality of cylindrical pedestals attached to the second skin. The pedestals are cooled by a cooling airflow metered into the space between the skins by apertures.
Gas turbine engines under development today must be capable of running at higher turbine operating temperatures to provide the improved efficiencies demanded by customers. The cooling air used to cool high temperature components represents a performance penalty, and the amount of cooling air must be minimized. While the above-mentioned patents address improved cooling efficiency and increased convection cooling surface area, engineers and scientists continue to search for ways to increase gas turbine operating efficiencies by using cooling air as efficiently as possible.